This application relates to the art of temperature responsive force transmitting mechanisms and, more particularly, to such mechanisms that collapse when a predetermined temperature is reached. The invention is particularly applicable for use with automatic sprinklers, and will be described with specific reference thereto. However, it will be appreciated that the invention has broader aspects, and can be used in other environments.
A known type of automatic sprinkler includes force transmitting means for releasably closing an outlet for fire extinguishing fluid. The force transmitting means is commonly a frangible glass bulb containing a substance that expands in response to thermal input for breaking the bulb. This opens the outlet for the fire extinguishing fluid.
In automatic sprinklers of the type described, when the glass bulb is the sole means for transmitting the force to close the outlet, the bulb must have a relatively high structural strength. This means that the bulb is less fragile, and its response time is relatively long, because a substantial pressure must build up within the bulb before it breaks. An arrangement has been proposed wherein approximately one-half of the force is transmitted through the glass bulb, and the other half through a rigid strut. However, even when one-half of the force is transmitted through the bulb, it must have a relatively high structural strength, and this significantly reduces its thermal response time.
It would be desirable to have an arrangement allowing the use of a highly fragile glass bulb having a very quick thermal response characteristic.